INGENIEUR
INGENIEUR
Figure 3 : Microbial fuel cell with two chambers ; anode and cathode ( PEM : proton exchange membrane ).
modification is not of interest , mixing these wild types of microbes together during fermentation is seen as an alternative method , which is termed Simultaneous Saccharification and co- Fermentation ( SSCF ). It doesn ’ t require sugar separation , and both glucose and xylose can be converted to ethanol . However , the drawbacks of mixed cultures include the difficulty in maintaining an optimum balance between both cultures , and the preparation of many inoculums before fermentation , which are a hassle for industrial applications . To overcome the limitations of using mixed cultures , genetic modification of a single microbe is desired to improve the feasibility of CBP method and improve the ethanol yield . This has been practiced by over expressing the genes from S . stipitis encoding xylose reductase ( XR ) and xylitol dehydrogenase ( XDH ) to enable xylose transportation into S . cerevisiae . Ethanol production was enhanced by over expressing the endogenous XK gene encoding xylulokinase . Another way is to carry out gene modification of natural ethanol producers to equip them with cellulotic properties . For example , yeast such as S . cerevisiae , P . stipitis , and various bacteria , namely Klebsiella oxytosa , Z . mobilis undergoing modification to include genes from cellulase producers ( Trichoderma reesei , Aspergillus niger ) to enable cellulase production .
From Lignocellulosic Biomass to Electricity
We can expand the potential utilisation of lignocellulosic biomass by transforming it into a more direct energy form , i . e . electricity . Green electricity , or some might term as renewable or sustainable electricity , has been extensively looked for all over the world . Green electricity is notably associated with electricity generator systems , for instance solar , wind and waterturbine energy systems that are now progressively being employed in commercialised projects by both developed and developing countries . Lignocellulosic based electricity in this instance , could also be one of those very promising near future green energy systems by incorporating it into a system called the bio-electrochemical system ( BES ).
One of the systematic tools in the BES principle is termed the microbial fuel cell ( MFC ). MFC is an emerging technology that generates electricity ( bioelectricity ) from biomass using bacteria . The liquid form of lignocellulosic or cellulosic biomass is oxidised by bacteria ( anaerobes and / or aerobes ) and the electrons released from the oxidation process are transferred to the electrode in an anode chamber and subsequently flows to a cathode chamber generating electricity ( Figure 3 ).
60 VOL 75 JULY-SEPTEMBER 2018